Energy saving and environmental protection have become the main focus in current automobile industry for new vehicle development. With this respective, the hybrid vehicle has turned into a main core technology and pursued by many automobile manufactures globally. Wherein, except the pure e-drive, the PHEV is one of the most fuel saving solutions, it has being advocated by many major automobile manufacturers. The PHEV primary consists of a relative lower displacement engine and one or two motors. Under normal vehicle running, the motor is generally responsible for providing pure electric power output and braking recycling energy at intermediate and low speeds, it also is used to achieve engine starting, while the engine can generate electricity by turning the motor when necessary, or take part in or boost power driving.
In current technology, the engine and the motor in the above-described plug-in type hybrid driving system are coupled mostly by the following ways:
I. Series solution: Such as GM Volt hybrid concept, it is a typical PHEV, The battery in the hybrid driving system can be charged by using the outlet of household power supply (e.g. 110V/220V). The PHEV can provide a longer pure electrically-driven travelling distance than a full hybrid electric vehicle. While when the battery power is dropping at a low level, the engine will automatically start to generate electricity through motor for battery charge to provide power, but the engine in this model does not take part in vehicle running operation directly. Under the long distance travelling condition, it required to convert mechanical (engine) energy into electric energy (thru motor/generator then store in battery), and then re-converting the electric energy into mechanical (driving motor) energy for power output. Therefore, the operational efficiency by the engine power is relative lower. Besides, in order to ensure acceleration/climbing performance of the vehicle, the demands on main traction motor and battery power are higher than the normal running condition, thus boosts higher cost on vehicle.
II. Parallel solution: Such as VW Phaeton GP2 hybrid vehicle. It is a driving-generating integrated machine, applying two clutches to connect the engine and conventional gear box. This hybrid vehicle design is simple in structure with lower cost. However, it can only be adapted to a large vehicle or rear driving vehicle, because the requirements on spatial dimensions of driving system inside the vehicle are high. Besides, the output power of the driving-generating integrated machine is generally not large enough, making it difficult to ensure the driving performance of the vehicle, when it is extensively driven by the pure electric drive mode.
III. Series-parallel Power Split solution: Such as Toyota Hybrid System (referring to CN patent application No. 200480019795.5, entitled “Power Output Device for Hybrid Vehicle”), and the Advanced Hybrid System proposed by General Motors Corporation (referring to CN patent application No. 200480038070.0, entitled “Hybrid Electromechanical Transmission of Complex Distribution Mode of Dual Mode Having Four Fixed Gear Ratios”), the engine and two motors are connected via one or more planetary gear systems, wherein power reconciling and gear shift are realized by power split principle in order to meet travelling requirements of the whole vehicle. However, power transmission path is complicated with this method, and there exists a power transfer loss phenomenon caused by unnecessarily converting mechanical energy into electric energy and re-converting the electric energy into mechanical energy for power output. Therefore, this method, when used in plug-in hybrid vehicle, will cause reduction of pure electrically-driven travelling distance.
F3DM type hybrid vehicle: This is another example, the vehicle is launched by BYD Holding Ltd. Using a relatively simple connection manner (referring to CN patent application No. 200610141069.1, entitled “Driving Device for Hybrid Vehicle”), the engine and a starting-generating integrated machine are linked together then connected them with another main motor via a clutch. Through the input shaft, the power flow is passing by a speed reducer or decelerator and then via the differential and finally reached to the axial shafts. This method is simple in structure, and under the ideal operational condition power is transmitted through directly; therefore, the transmission efficiency is high. However, under the real driving condition, when the vehicle is in purely electrical drive, it is very difficult to meet all design requirements in terms of climbing, acceleration performance and maximum electric travelling speed simultaneously, since the main decelerator drives the vehicle directly. In general, a large torque and high speed motor must be employed, that makes the demands on functions of electronic (electric) power controller and battery system for matching with the motor increase accordingly. Even so, it is very difficult to ensure the motor could often operate in a higher efficiency region under the urban traveling condition. In addition, in case when the energy of battery is low, so it is required to change into motor/engine hybrid travelling mode, but due to restrictions on minimum stable rotation speed and torque characteristics of engine, the engine will only be able to operate in a way like that in the above described series mode in many travelling conditions, such as when confronted with intermediate and low speeds urban road and ramp road conditions, thus reducing energy utilization efficiency greatly.